1. Field of the Invention
The present invention relates to capacitors in general and in particular to an optimally or critically damped capacitor and a method of making the same.
2. Description of the Prior Art
All capacitors are composed of parasitic components such as resistance R.sub.S and inductance L.sub.S as shown in FIG. 4 herein. The value of R.sub.g and L.sub.s depends upon the materials and construction methods used to make the capacitor. The parasitic inductance L.sub.S and capacitance C of a typical capacitor will form a series resonant circuit at a particular frequency and if the values of L.sub.S and C are known, the resonant frequency can be calculated by the well known formula: ##EQU2##
When an applied signal voltage or current has a frequency component at or very near the resonant frequency, the series resonance will be excited and a sustained oscillation will occur. How long the oscillation will persist depends upon how much dissipative resistance (R.sub.S) is present. The presence of resistance, R.sub.S, causes the oscillation voltage or current at resonance to decay towards zero. This is called a "damped" oscillation. For example, FIG. 5 herein shows a lightly damped or underdamped oscillation of a capacitor which has had its resonance excited. This oscillation is also called "ringing". Prolonged oscillation or ringing is very undesirable when it occurs in circuits that are required to have minimum waveform distortion. An underdamped capacitor or capacitive circuit condition exists when: ##EQU3##
In contrast to an underdamped condition, an overdamped capacitor or capacitive circuit exhibits a long generally non-periodic discharge time as shown in FIG. 6. The overdamped condition exists when: ##EQU4##
A capacitor or capacitive circuit is considered critically damped as shown in FIG. 7 when: ##EQU5##
While the electrical characteristics as shown in FIGS. 5-7 of underdamped, overdamped and critically damped capacitors and capacitive circuits are generally understood, critically damped capacitors, such as those made with low loss or high Q dielectrics such as plastic film, ceramic and mica, are generally not available as single integrated electrical components. Consequently, it has been necessary for a person desiring to make a critically damped capacitor or capacitive circuit to use a conventional low loss or high Q dielectric capacitor together with a proper amount of discrete series resistance; the amount of reqired resistance being determined usually by time consuming and costly trial and error.